Erasers were invented in 1770 by an engineer named Edward Nairne. Nairne used rubber from trees, and his magical device was so impressive that the theologan Joseph Priestley mentioned it in a footnote in his book A Familiar Introduction to the Theory and Practice of Perspective: "I have seen a substance excellently adapted to the purpose of wiping from paper the mark of black-lead-pencil,” he wrote. Since then, as material engineering has improved, erasers have become more high-tech.
But even among eraserheads, the exact composition of today’s erasers is a bit of a mystery. Precise breakdowns of materials tend to be guarded as company secrets. Rigoberto Advincula, a professor at Case Western Reserve University who has consulted in the pencil and eraser industry, said that erasers are usually made of some combination of rubber and plastic components. Natural rubbers—made from the stuff that comes from rubber trees—have good erasing properties. Thermoplastics, a type of polymer that can be hardened or softened depending on heat, are easier to shape. A host of additives, like additional particles and aromatic agents, can tweak the mixture further, as can the compounding process. The erasers we see in stores are almost always some proprietary combination of all three.
Natural rubbers make the best erasers, because their innate abrasive qualities help them remove material from paper with aplomb, Advincula said. The cheaper plastics that have been embraced by eraser manufacturers—including PVC, which raises environmental concerns too—are the ones that cause problems, because, well, you get what you pay for.
In the end, cheaper raw materials like bottom-of-the-line thermoplastics and synthetic rubbers beget cheaper, and worse, erasers. Charles Berolzheimer, CEO of CalCedar, a supplier of wooden slats for pencils, attributed the decline in eraser quality to globalization. As companies focused on keeping prices down, they moved their manufacturing to Asia and sought out cheaper materials. The cheaper the pencil, the cheaper the eraser, so upgrading your pencil (or upping your separate eraser budget) might be one way to guarantee improvement.
You might be inclined to try and find vintage erasers, from the good old days before polymer contamination. But that wouldn’t work either. While a pencil from 1770 would, after a rejuvenating sharpening, still work, an eraser from that same time would not. Johnny Gamber, who co-hosts the Erasable podcast with Welfle and keeps a blog called Pencil Revolution (and who likes either the Faber-Castell white plastic eraser or the Staedtler Mars white plastic eraser), pointed out that, “erasers age, pencils don’t. You can use a hundred-year-old pencil and sharpen it and it will work just fine. You can’t really stock up on erasers because they dry out.” (This idea inspired the slogan on a t-shirt the Erasable podcast sells: “Pencil is forever.”) Advincula explained: “Over time, some of the rubber properties can be lost because of oxidation or chemical degradation. Some of the plastic can also soften or even harden because of different environmental conditions.” In short, exposure to air and light is doing your erasers no favors.